T4: Characterization of early T4 mRNA will continue with particular emphasis being placed on determining the size of specific immediate early mRNAs. This analysis will be carried out by preparative polyacrylamide gel electrophoresis of the RNA followed by translation of the fractionated RNA and analysis of the radioactive polypeptides synthesized in vitro by SDS-polyacrylamide slab gel electrophoresis. RNA will be analyzed at different times during T4 infection in the presence or absence of the antibiotic chloramphenicol in order to determine whether any change in size of the RNA occurs. T7: The transcriptional mapping of the T7 late region will be continued to determine the initiation and termination points of the major transcripts. In addition we will attempt to isolate a mutant defective in producing the T7 DNA unwinding protein. Locating the gene for this protein will help clarify the location of the transcripts containing the mRNA for gene 3.5 and other mRNAs in this region. The effect on translation and size of treating T7 mRNAs isolated from E. coli BL 107 (RNase III-) with RNase III will be studied. Yeast: The size of specific yeast mRNAs will be studied by in vitro translation of fractionated yeast mRNAs followed by electrophoretic and immunological analysis of the radioactive polypeptides synthesized in vitro in a wheat embryo cell-free system. Attempts to isolate active yeast mRNA from nuclei will continue with reference to determining the size of a specific yeast mRNA whose cytoplasmic counterpart has been identified. BIBLIOGRAPHIC REFERENCES: Pachl, C. A. and Young, E. T. Detection of Polycistronic and Overlapping T7 Late Transcripts by In Vitro Translation. Proc. Nat. Acad. Sci. USA 73, (1976). Young, E. T. and Menard, R. C. Analysis of the Template Activity of Bacteriophage T7 Messenger RNA during Infection of Male and Female Strains of Escherichia coli. J. Mol. Biol. 99, 167-184 (1975).